Hello neutrino,
thank you for your reply. I'm not sure "Quantity Revise" match our needs. Can you explain me how "Quantity Revise" work? I mean, which direction? From ebay orders to decrease Magento stock, from Magento Stock to update items quantity on ebay or both?
Don't worry about overselling. We are a production company, we don't have anything on stock, so we would use the new attribute "Ebay quantity" to decide for each sku how many items to sell. So we expect M2E Pro use this field to update ebay, but from the order side we would avoid an order can decrease this field.
Is it possible? How?

Hello Neutrino, thank you for your answer.
No, you didn't understood. I don't want to use this function, I would to decide the *exact* quantity of item to sell for each product I have and this quantity should never change on ebay also if the item is sold. To do this I created the attribute "Ebay quantity" who is the *exact* quantity I would to sell and who I never would be decreased by M2E Pro after a selling. I hope now it is ore clear

Hello, I'm using Magento 1. due to stupid limitations from ebay, I created a new attribute "Quantity ebay" who I would to use as "limit" of the items to listing on ebay and I configured the policy on my ebay listing to use it: http://snpy.in/9KzfMU
This work perfectly, the problem is: when one item is sold, M2E decrease the quantity on the field "Quantity ebay", there is a way to avoid it?
Thank you in advance! A virtual beer for the fastest answer